Basic zinc dialkyl dithiophosphates and methods of making the same



of atmospheric oxygen thereon. present invention is directed to theantioxidants, per se;

. 2,794,780 BASIC ZINC DIALKYL DITHIGPHDSPHATES AND METHODS OF MAKWG THESAME Vernon P. Wystrach, Darien, and Edwin 0. Hook and George L.Christopher, New Canaan, Conn, assignors to American Cyanamid Company,New York, N. Y., a corporation of Maine No Drawing. Application March25, 1954, Serial No. 418,792

, 11 Claims. (Cl. 25232.7)

The present invention relates to the stabilization of organic substancesagainst polymerization, oxidation, and other forms of deteriorationresulting from the action More specifically, the

to the processes of preparing them; and to the organic compositionscontaining the same.

It is well known in the art that the development of such undesirableoxidative effects may be deterred by the addition of small quantities ofstabilizers or antioxidants to organic substances which are normallyliable to oxidation and other deteriorative effects. Among the organicsubstances which have been so stabilized by such antioxidants have beenoils, waxes, hydraulic fluids; textile softeners; paints and varnishes;petroleum products including lubricating oils, turbine oils, transformeroils, cutting oils, etc.; plastic molding powders; and the like.

More specifically, it is known that in modern internal combustionengines, including diesel engines and particularly those using highsulfur fuels, as well as aviation engines and ordinary automotive sparkignition engines, various products of combustion fuel and oildegradation,

condensation, polymerization, and the like, are generally formed whichcause piston ring sticking, valve sticking, and corrosion of variousmetal parts of the combustion zone and auxiliary parts functioningtherewith. The development oflacquer and/or carbonaceous deposits on therings and grooves and on valve stems and valve guides appears to be themost probable reason for ring and valve sticking. The production ofacidic bodies by the chemical combustion of the fuel and/or by thedegradation of the lubricating oil as by partial oxidation and the likeappears to be responsible, at least in part, for the corrosion of theengine parts associated withthe combustion chamber and lubricated bymeans of the same lubricant utilized in the lubrication of the pistonrods, pistons, and the like. Also, the acidic oxidation productsdeveloped in the lubricating oil appear to exert a catalytic effect inthe oxidation of the lubricating oil hydrocarbons.

The addition of various types of metal derivatives of organic compoundsto lubricating oils is known and practiced to minimize the difficultiesalready referred to and to improve the properties of these oils in otherrespects. Thus, for example, basic materials, such as basic metalcompounds, have been used to provide an alkaline reserve to neutralizethe developed acidic compounds.

It is also known that calcium and other polyvalent metal salts ofpetroleum or synthetic sulfonic acids have been used as engine oildetergent addition agents and that the corresponding basic(hydroxylsalts have been used additionally for their basicity asneutralizing agent for the acidic bodies developed in the lubricant,regardless of their source. 7

It is an object of the present invention to provide a new class ofantioxidants for the stabilization of organic substances in*- generaland specifically as addition agents in oils which are to be used ascrankcase lubricants for internal combustion engines. These compoundsexhibit to a high degree the desirable properties of inhibiting thedevelopment ofcorrosivity in the organic substance or oil, of improvingoxidation stability of the oil, and of 2 promoting general cleanlinessand reducing ring sticking, piston skirt varnish formation, and thelike, when used in an engine.

-We have found that thisobject and others which will become clearhereinafter may be accomplished by the use of a novel class ofantioxidants falling with the chemical group of basic zinc dialkyldithiophosphates having the following general structural formula:

wherein R is a normal or secondary alkyl radical having from 1 to 18carbon atoms.

We have further found that the basic zinc salts of the present inventioncomprise a source of reserve alkalinity whereby the acid materialsdeveloped in or by the lubricating oil during actual operation isneutralized and its deleterious effects avoided.

It is, of course, to be appreciated, that, when the antioxidant is usedin aspecific application or for a definite purpose, such as animprovement additive in a hydrocarbon lubricating oil, it is necessarythat the antioxidant be soluble in such substance to a suflicient degreeto exhibitits desired antioxidant characteristics and properties. It isalso to be observed that the amount used in any particular instance willvary as to the nature of the organic compound to be stabilized, thepurpose for which it is to be used, etc. When used as an antioxidant inlubricating oils, amounts of from about 0.1% to about 5% by weight maybe used, although, more commonly from about 0.4% by weight to about 2%by weight have been employed. When used in combination with otherantioxidants or detergents, lesser amounts may be found adequate.

The radical R in the .above structural formula may be any normal orsecondary alkyl radical such as methyl, ethyl, propyl, isopropyl, butyl,4-tnethyl-2-pentyl, hexyl, octyl, decyl, dodecyl, tridecyl, tetradecyl,octadecyl, hexadecyl, etc.

These zinc basic salt compounds are to be distinguished from the normalzinc salts which do not possess such alkaline reserve properties andthese distinctions will be brought out in the following examples ofpreparations and evaluations of the resulting products. It should beunderstood, however, that although these examples and evaluations maydescribe in particular detail some of the more specific features of theinvention, they are given primarily for purposes of illustration and theinventive concept in its broader aspects is not to be construed aslimited thereto.

EXAMPLE 1 n-Butyl alcohol (222 grams 3.0 moles) was reacted with 166grams (0.75 mole) of phosphorus pentasulfide on a steam bath forapproximately ninety minutes. The purity of the resulting di-n-butyldithiophosphate acid was 90%,

of a filter aid, such as Hyflo, were added, the solu-' tion wasfiltered, and 68 grams (0.50 mole) of zinc chloride in 40 grams of waterwas added to the filtrate- The resulting mixture was heated at C. forseveral minutes.

Patented June 4, 1957 The temperature rose from room 1 Twenty-five gramsof an activated The product was then separated from the f aqueous phase,stripped, and filtered througha coated,

' 3 steam-jacketed funnel. The yield, before the final 'filtration, was233 grams.

After standing at room temperature, the filtered re action productseparated "into a solid and a liquid phase.

4 The basic isopropyl salt was a white crystalline solid, whereas then-hexyl and n-decyl derivatives were yellow viscous liquids and wereworked upvia solution in hexane followed by drying over sodium sulfateand evaporation The solid phase was repeatedly washed with cold meth- 5in air-stream. Analyses o these P u are Presented anol, giving a whitecrystalline product. It was insoluble in the followin teblein'me'thanol,quite soluble in hexane and very soluble in diethyl ether. I I AnalysisA final purification was made by dissolving the solidDmlkylDlthlophosphate in hexane, filtering off the insolubles, addingmethanol C c ate Found until incipient precipitation resulted andallowing the solvent to evaporate at room temperature. The resulting I ePee residue was composed of large, frangible, off-white crystals REmplr' 9 2, 3;? cent which melted at 145-153" C.

i-Propyl C1sH43P307SnZI12 16.6 11.8 24.4 fif li fi ia fii'ijziz: fifiilfi fdisfi z iiifi: 3:? 213 i353 8:7 30 n CalculatedtorG H P O S Zn,15.0 10. 7 22.1 An acid titration of thesolidmate i derived flem theFoundforO24H55P307S6Z117 151 1045 preparation of basic Zinc dibulyldithiophosphate (a 1.2131 gram sample in ml. ether and 60ml. ethanol)The Sehd was basic and e Sample was titrated With required 13.75 ml. of0.100 N HCl, the endpoint occurstandard acid. A mixture of onepart-diethyl ether and i at H 4 5 U i th va1 es,.it an be calculated WParts ethanol Was a Satisfactory Solvent for this titfathat the strongacid neutralizing ability of the above basic Based. on Such a titration,the equivalent Weight 25 zinc dibutyl dithiophosphate corresponds tothat of a Of the material Was 882 y Titration of the conventional basicpetroleum sulfonate having a neutrasolid with standard alkali gave aneutral equivalent of 283 li ti number of about 63. y Which isapproximately One-third of that Representative antioxidant compositions,some comobtained by titration with acid. These values are in prising thenormal salt of Zinc di-n-butyl dithiophosphate very good agreement withthe possible structure based on 3 and others comprising the basic saltof thisinvention were the ahalysie used in comparative tests to inhibitthe oxidation of a white mineral oil. The test 'was carried out asfollows: EXAMPLE 2 300-gram portions of the mineral oil were weighed out5 and to each was added approximately 0.1 gram of the ll 1representative vsalt. The mixtures were placed [in cylin- 3(CHO)ZPSH4N1OH Zznch drical glass vessels 40 cm. diameter x7400 cm. height H iwith a fritted-glass air-inlet tube at the bottom and an (C4H9O)QPS z 'zp 4N g1 311,0 exit-gas tube at the top. The vessels were then placed 2in a thermostated bath, controlled at 155 C. and pure 24.2 g. (0.1 mole)-di-n-butyl dithiophosphoric acid (N. E.. 40 nitrogen bubbled throughthe solution at 200 cc. per min- 241.9) ute for l'hour, during whichtime the solutions reached 9.1g. (0.067 H1016) zinc chloride theb'athtemperature- 5.5 g. (0.133 mole) 97% di h d id The gas stream wasthen switched to air at 200 cc. 'per minute and the time noted. Theoutlet gas stream was i Sodlum hydroxld? was dlssolved 200 of thenpassed through apa'ramagnetic type oxygen analyzer, water and grams ofwe Was added, after Wh1ch the dibutyl dithiophosphoric acid was added Asolution of Where oXyg-en content was meas'umd and reForded as I theZinc chloride in 50 m1 of water alas then added a function of time. Thetime at which the solution began slowly with manual stirrin A solid crstalline reci ito absorb oxygen was noted by the rapid m the tate formedimmediately D. After air-dr in the watgroxygen cor-Item of the Outletgas m Thlsmfe can Washed pmduct a yield 26 0 rams g g of whit 50 bedeterm1ned very accurately and is recorded in the crystalline solid wasobtained it a eare d t o be ident i table as the mducnon penodzn bemgnumber 9f cal ith th e l d P 2 t f E 1 minutes elapsed between theswitch from nitrogen to air, w e Pr y escn Pro uc o m e 1 and the rapiddrop in the oxygen content of the outlet and had the following analysis:15.1% Zn; 10.5% P; gas stream 20.8% S.

EXAMPLE 3 Additive Induction Period 011 Appearance Three representativepotassium dialkyl dithiophospha'tes lkyl=is0pr yL llljyl, r n-l yl) werconverted to gone piai i ia 1 68s than mins dark. e correspon ing asiczinc sa ts by dissolving them in 5e 15 darkwater, adding additionalalkali, and finally adding the B351 975mm amount of Zn ion prescribed bythe equation below. Although We have described but a few specific examPreparation of basic zinc dialkyl dithiophosphates ples of ourinvention, we consider the case not to be limited thereby nor to thespecific substances mentioned 3 R0 ,PssM MOH 2211012 therein, but toinclude various other equivalent com- KRO)ZPSS JIZI1-HOZHSSP(OR)H 4MC1pounds of similar constitution as set forth in the claims [M= M appendedhereto. It is understood that any suitable M M ghangels or variationsmay be made without departing 1-0 -0 Yield rom t e spirit or scope ofthe inventive concept. Alkyl Group (R) Ksalt,g. 11118, Nag-H, Z2312,Weclaim: 4 I

g. e t 1. A basic zinc dithiophosphate having the formula RO S S 0-Rsnarl-.- :1 it? a: as as as 32:? I P n-Deeylu 13.5 100 10.0 10.0 11.683.9 v

. RO S- gn.HOZn-S 0R wherein R is a member of the group consisting ofnormal and secondary alkyl radicals containing from 1 to 18 carbonatoms.

2. A basic zinc dithiophosphate as defined in claim 1 in which R isbutyl.

3. A basic zinc dithiophosphate as defined in claim 1 in which R isisopropyl.

4. A basic zinc dithiophosphate as defined in claim 1 in which R ishexyl.

5. A basic zinc dithiophosphate as defined in claim 1 in which R isdecyl.

6. A hydrocarbon mineral lubricating oil composition comprising arelatively large proportion of a hydrocarbon mineral lubricating oilhaving dissolved therein a relatively small amount from about 0.1% toabout 5% by weight, sufiicient to inhibit deterioration of the oil byoxidation, of a basic zinc dithiophosphate having the formula wherein Ris a member of the group consisting of normal and secondary alkylradicals containing from 3 to 18 carbon atoms.

7. A hydrocarbon mineral lubricating oil composition comprising a basiczinc dithiophosphate as defined in claim 6 in which R is butyl.

8. A hydrocarbon mineral lubricating oil composition comprising a basiczinc dithiophosphate as defined in claim 6 in which R is isopropyl.

9. A hydrocarbon mineral lubricating oil composition comprising a basiczinc dithiophosphate as defined in claim 6 in which R is hexyl.

10. A hydrocarbon mineral lubricating oil composition comprising a basiczinc dithiophosphate as defined in claim 6 in which R is decyl.

11. A method of preparing a basic zinc dithiophosphate having theformula References Cited in the file of this patent UNITED STATESPATENTS Freuler Dec. 5, 1944 Funk Dec. 26, 1950

6. A HYDROCARBON MINERAL LUBRICATING OIL COMPOSITION COMPRISING ARELATIVELY LARGE PROPORTION OF A HYDROCARBON MINERAL LUBRICATING OILHAVING DISSOLVED THEREIN A RELATIVELY SMALL AMOUNT FROM ABOUT 0.1% TOABOUT 5% BY WEIGHT, SUFFICIENT TO INHIBIT DETERIORATION OF THE OIL BYOXIDATION, OF A BASIC ZINC DITHIOPHOSPHATE HAVING THE FORMULA